In the related art, on an electric motor vehicle such as an electric automobile which travels by using power, a drive battery that stores vehicle drive power (which is referred to as “drive power”, hereinafter) at high capacitance and high voltage, and an auxiliary device battery that stores the drive power (which is referred to as “power for auxiliary device”, hereinafter) of an auxiliary device within the vehicle at a battery voltage of approximately 12V in general have been mounted. Here, charging of the drive battery is carried out by supplying an external power source (commercial power source) from a charging port which is arranged in a vehicle body of the electric motor vehicle. Moreover, the charging of the auxiliary device battery is carried out by stepping down and supplying the power within the drive battery with a DC/DC converter.
As a power supply device to the auxiliary device battery in the vehicle, for example, a technology such as PTL 1 or PTL 2 described below is known. In an auxiliary battery power feeding system of PTL 1, an auxiliary battery power feeding converter of which capacitance is smaller than that of a main DC/DC converter is included, and the auxiliary battery power feeding converter generates a second low voltage for applying to an auxiliary battery separately from the main DC/DC converter. When the power is fed to the auxiliary battery at the time of stopping the vehicle, a power feeding control circuit applies the second low voltage from the auxiliary battery power feeding converter to the auxiliary battery, by switching and controlling a low pressure path switching unit. Thereby, it is possible to efficiently feed the power to the auxiliary battery.
Moreover, PTL 2 is a power source system in which the charging is possible by using the power from an external power source, and an auxiliary device battery supplies a power source voltage which is lower than an output voltage of a power storage apparatus to an auxiliary device load. A DC/DC converter supplies the power source voltage to the auxiliary device load and the auxiliary device battery, by stepping down the power from the power storage apparatus. An AC/DC converter uses the power from the external power source, and the supply of the power source voltage to a charging ECU and the charging of the auxiliary device battery are possible. Therefore, at the time of the external charging, an HV-ECU controls the charging power of the power storage apparatus and the charging power of the auxiliary device battery, based on a charging state of the auxiliary device battery. Thereby, in the vehicle in which the charging is possible by the external power source, the lowering of charging efficiency at the time of the external charging is suppressed.